JEE Chemistry 2025 Question with Solution

Given: A cyclic compound containing a cyclopentene ring, one hydroxyl group and one ethyl group.

Find: The correct IUPAC name.

For cyclic compounds, numbering starts from the carbon bearing the highest-priority functional group. Here, -OH has higher priority than the double bond, so the carbon attached to -OH gets locant $1$.

The ring is then numbered to give the double bond the lowest possible locant. This places the double bond at $2$, giving the parent name cyclopent-2-en-1-ol.

The ethyl substituent is then found at carbon $4$.

Therefore, the correct IUPAC name is 4-Ethylcyclopent-2-en-1-ol. The correct option is D.

Given: The structure is a cyclopentene ring with a double bond, an ethyl substituent, and a hydroxyl group.

Find: The systematic IUPAC name.

1. Identify the parent ring: it is a cyclopentene ring.
2. Identify the principal functional group: the hydroxyl group has priority over the double bond in numbering.
3. Assign carbon $1$ to the carbon carrying -OH.
4. Number the ring in the direction that gives the double bond the lowest locant; this gives cyclopent-2-en-1-ol.
5. Locate the substituent: the ethyl group is at carbon $4$.

Hence, the full name becomes 4-Ethylcyclopent-2-en-1-ol.

The solution notes the same final result, although it mistakenly mentions a cyclohexene structure in one sentence. The derived name from the working remains 4-Ethylcyclopent-2-en-1-ol.